Fix cooling in C4

This camera, at least mine, does not cool down when setting temperature
to 100C. Instead it starts cooling at 100%. I guess, this is caused by
a integer overflow (making 100C a large negative value). Setting the
temperature to 50C is accepted by the camera and works as intended.

indi-mi/mi_ccd.cpp

@@ -31,7 +31,7 @@
 #include <utility>
 
 #define TEMP_THRESHOLD  0.2  /* Differential temperature threshold (°C) */
-#define TEMP_COOLER_OFF 100  /* High enough temperature for the camera cooler to turn off (°C) */
+#define TEMP_COOLER_OFF 50   /* High enough temperature for the camera cooler to turn off (°C) */
 #define MAX_DEVICES     4    /* Max device cameraCount */
 #define MAX_ERROR_LEN   64   /* Max length of error buffer */